Control mechanisms for intracellular calcium levels in fibroblasts will be examined in the context of their role in regulating cell motility. Specific attention will be given to the potential role of the plasma membrane in regulating calcium concentrations over levels known to induce contraction in muscle. The permeability of the plasma membrane to calcium and active transport of calcium by the plasma membrane will be examined in this context. Isolated plasma membrane vesicles will be used in this work. Further evidence for the role of the plasma membrane in controlling motility will be sought in living cells by altering the permeability of the membrane to calcium and inhibiting active transport of calcium by the membrane. Cinemicrographical techniques will be used to record these studies.